1. Field of the Invention
The present invention relates to cockpit displays and more particularly to automatic adjustment of the brightness of cockpit displays.
2. Description of the Prior Art
There are several systems available which control brightness of video instruments. One such system is disclosed in U.S. Pat. No. 4,589,022 to Prince, J. S. et al titled "Brightness Control System for CRT Video Display". The control system includes a buffer amplifier for receiving high speed video information, a gain control variable resistor serving as a contrast control, an ambient light sensor for driving a nonlinear amplifier to provide an ambient light signal, and a manual brightness control potentiometer which is adjustable to provide a constant brightness signal. The video information signal, the ambient light signal, and the manual brightness control signal are added together by a summing device. An exponential transfer function then transforms the resulting signal into brightness levels compatible with human eye brightness detection.
The present invention differs from the prior art in that it seeks to use the ambient light signal to maintain a constant contrast (actually extrinsic contrast) despite changing ambient light conditions. In addition, the present invention is independent of a specific hardware implementation and is applicable to a wide variety of CRTs, and even non-CRT displays including Heads Up Displays (HUDs).